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<title>6.21.2.3 Handling boolean (flag) options
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<H3><A NAME=
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"optparse-handling-boolean-options"></A>
6.21.2.3 Handling boolean (flag) options
Flag options--set a variable to true or false when a particular option
is seen--are quite common.
<tt class=
"module">optparse
</tt> supports them with two separate
actions,
<code>store_true
</code> and
<code>store_false
</code>. For example, you might have a
<code>verbose
</code> flag that is turned on with
<code>"-v"</code> and off with
<code>"-q"</code>:
<div class=
"verbatim"><pre>
parser.add_option(
"-v",
action=
"store_true",
dest=
"verbose")
parser.add_option(
"-q",
action=
"store_false",
dest=
"verbose")
Here we have two different options with the same destination, which is
perfectly OK. (It just means you have to be a bit careful when setting
default values--see below.)
When
<tt class=
"module">optparse
</tt> encounters
<code>"-v"</code> on the command line, it sets
<code>options.verbose
</code> to
<code>True
</code>; when it encounters
<code>"-q"</code>,
<code>options.verbose
</code> is set to
<code>False
</code>.
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<span class=
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2.4.2, documentation updated on
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2005.
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